I have been puzzling over a mineral which was found in the Dundas Quarry (North Section) for a while. I picked up a large rock ~80 pounds, and smashed it into smaller bits roughly 5 years ago. The rock was heavily oxidized brown and contained numerous Galena cubes, Calcite crystals, and what appears to be spherical Sphalerite crystal growths around a yellow mineral (possibly sulphur). Sphalerite is also noted on the specimen.

Then there is this mineral, which is much smaller than 1 mm, so scratching it would be impossible. It does not fluoresce under short or long wave UV, and forms tapering crystals with hexagonal cross-section. It is red to brown, and also yellow to orange. as shown in the attached photos.

I was leaning towards Wurtzite as...

1) Sphalerite and Wurtzite are of the same formula, and Sphalerite is quite common in this quarry.2) The colour and shape are very similar to that of specimens of Wurtzite in the MINDAT gallery,3) Some of the crystals are on the outside of the spheres have these crystals attached to the Sphalerite balls, which would be fitting with a collophorm texture (checking my textbooks from back in my geolab days), which are Sphalerite with Wurtzite and Sulphur.

In the viscinity of the mystery crystals are Galena cubes as well as Dolomite crystals.Any thoughts would be greatly appreciated.

Hi Andrew I am not familiar with the occurrence, but beside wurtzite wich is a good guess, your description (red or yellow hexagons stacked in inverse pyramids) and the paragenesis could also fit greenockiteGreetings from BelgiumAlain

I have to admit, Greenockite was another thought I had, though, how would you determine if it was one or the other. The association with the Galena, and the fact that it in oxidized rock (dolomitic limestone hostrock, with occasional shaley zones predominantly in this quarry) lead me to believe that the crystals may be more than just Sphalerite. Oh, and the crystal form doesn't conform to anything else I have seen there.

I had been puzzling over this one for a while. There was no record of Wurtzite at this quarry, but all the signs pointed that way. It's always good when your gut feeling seems to be right. That being said, I have been in contact to a collector in the states who would get it analyzed. Never hurts to be 100% sure.

The crystals have been sent in for analysis (attached). The crystals sent in were described as "Long, thin with smooth faces, but different from Sphalerite". The Fe spike is in excess of 8% I am told, though Wurtzite is up to 8%.

I am unfamiliar to this analysis, so I put it out ... What are these crystals, Wurtzite? What ever we come up with, I will set up in Mindat.

The Chemical Analysis indicates Sphalerite or Wurtzite, but the crystal shape is clearly not Sphalerite (6 sided and tapering). Would this then indicate Wurtzite without the XRD as Sphalerite does not do this?

There are 3 images of specimens from this locality showing a yellowish-white material labeled 'Dolomite'. This was tested and verified by the Royal Ontario Museum as barite 8 years ago. It was tested and again verified at the ROM in the past year by Tony Steede as BARITE.The purple colouring is definitely caused by the presence of fluorite.

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